In Of Mice and Men, Curley's wife visits and starts a fight for a couple of reasons, one obvious and one psychological.
Obvious reason: Steinbeck wants her to. She's a character, a minor character at that. She doesn't even have a name. She's the only female character in the novella. She's an archetype: a temptress. Temptresses tempt. They tempt men. What else is she going to do? Sing and dance? She's got to visit the bunkhouse, the barn, the stable. She's got to start a fight. These men are animals, and she's just the thing to get their blood boiling. Even when she's not there, she's there starting a fight.
Psychological reason: she's lonely. She wants attention from Curley, but he's not giving it to her. So, she seeks it from the others. There's two new guys, one big and one small, and she's curious. Maybe she wants to make Curley jealous by seeing her talk to the big buy because she knows Curley hates big guys. But that might get her beat up, so I don't think she would want that. So maybe she wants to see Curley beat up someone else.